Mikael Jonsson

Experimentally determined transient and residual stresses in a butt-welded pipe

Abstract Single pass butt-welding of a pipe is studied. Low heat input has been used to obtain high cooling rate with adherent martensite in the final phase transformation in the heat affected zone. Strains and stresses have been measured during and after welding on the pipe outer surface. Deviations from rotationally symmetric strain and stress fields in the pipe are studied. Two different analytical solutions for the residual stress field from the literature are discussed. The experimentally obtained residual stresses are compared with those analytical solutions. Qualitatively good agreement between experiments and analytical solutions was obtained, although the analytical solutions do not consider effects of phase transformations.

Optimization of acoustic response

The expression “acoustic optimization” can be applied to numerous different disciplines within the field of acoustics. From seismic waves, sound in the atmosphere through bioacoustic, psychoacoustics, and room and theater acoustics over shock and vibration in mechanical structures. This paper deals with the latter. Sound generated by vibrating structures is often called noise which is to be minimized. However, not all vibrating structures produce noise, for example the violin is also a vibrating structure that in most peoples opinion produces sound called music. In the case of the violin, great effort is made not to minimize but to optimize the sound, i.e. to get the “right” sound out of the structure. Acoustic optimization within this discipline involves automatic changes of structural design variables to obtain minimum or specified sound in specified regions inside or outside the structure. Examples of problem formulations and some theoretical considerations in the field of acoustic optimization in connection with vibrating mechanical structures will be pointed out. Four simple test cases are included as numerical examples of the method proposed.

Deformations and Stresses in Butt-Welding of Large Plates With Special Reference to the Mechanical Material Properties

Simulation of automatic butt-welding of large plates was investigated. Two different steels were considered. The plates were tack-welded before the butt-welding. The simulation includes the tack-welding, the butt-welding and the cooling to room temperature. The simulations should lead to an understanding of the mechanics behind the change in gap width in front of the moving arc, which is of importance in automatic welding production. The residual stresses due to the butt-welding were also studied. The magnitude and the distribution of the residual stresses are important in design of welded structures. The change in gap width in front of the moving arc and the residual stresses depend on the material in the plates, the restraints of the plates, the size of the plates and the welding parameters. The most important welding parameters are the arc energy per unit length of the weld and the welding speed. The change in gap width depends also on the tack-welding procedure.

TRANSIENT AND RESIDUAL STRESSES IN A SINGLE-PASS BUTT WELDED PIPE

The development of stresses and strains during butt welding of a thin walled pipe is followed numerically by use of the finite element method (FEM) and, in parallel, measured experimentally. Three different FE-models of the pipe, one fully three dimensional, one rotationally symmetric and one shell type, were used in the numerical part of the study. For all three models the pipe material was taken as thermo-elasto-plastic with strongly varying temperature dependent material properties. Calculated results for the weld metal and HAZ were found to be heavily dependent on the constitutive modelling of the final phase transformation. The qualitatively best agreement with the experiments for the residual stress field was obtained with a simplified FE-model which did not consider such effects. During welding, the transient stress field was found to be strongly rotationally nonsymmetric.

Computational Model of Flame-Cutting

A computational model for simulation of flame-cutting has been developed. Two different cutting conditions are compared with respect to the residual stresses. The first case is a plate cut at room temperature and the other is the cutting of a preheated plate. The model depends on measured micro-structure to estimate the required heat input. The model is verified by comparing the calculations for the preheated plate with experimentally obtained residual stresses. Lower residual stresses in the preheated plate prevents subsequent cracking.

Measuring True In-Plane Displacements Of A Surface By Stereoscopic White-Light Speckle Photography

When in-plane surface deformations are measured using white-light speckle photography, errors arise if an out-of-plane displacement is present. Stereoscopic photography resolves this problem and makes possible the measurement of true in-plane displacements. A rigid-body translation is introduced to determine unambiguously the direction of the displacement.

Measurement of residual deformations in butt-welded plates by use of the white light speckle technique

Abstract A method to measure residual deformations in welded plates is presented. An optical technique, called white light speckle, is used to record the released residual deformations. The method is destructive. Two experiments have been performed. The results are compared with corresponding calculated values. A short description of the calculations is given.

Measuring 3-D displacement of a surface using the white light speckle technique

When measuring in plane surface deformation using white light speckle photography, errors will arise if an out of plane displacement is present. Here it is shown that stereoscopic photography resolves this problem and makes the measurement of true in plane displacements possible. A rigid body translation is also introduced to determine unambiguously the direction of the displacement.

A force transducer based on measurement of mean strain in a compact body

Abstract A force transducer based on measurement of mean strain in a body has been developed. The transducer can be made stiff and compact and is therefore suitable for measurement of impact forces as well as static forces. An experimental test of a simple first prototype was performed using both static and impact loads with different distributions over the load-carrying area of the transducer. The results of the experiments show that the requirement of insensitivity to differences in load distribution is acceptably fulfilled. Improvements are expected to be possible if the transducer is made in a more accurate way.